Cold temperatures have negative effects on battery packs. For example, lithium ion battery packs generally lose substantial discharge capacity at sub-freezing temperatures and are even susceptible to irreversible damage if charged in sub-freezing temperatures. In order to maintain optimal performance in sub-freezing environments, heating modules may be provided with a battery pack to maintain minimum operating temperatures. However, these heating modules can add significant mass to the assembled battery pack and often have high watt densities that form localized hot spots.
Heaters meant for batteries are fairly uncommon and tend to be supplied as an afterthought to be installed as an independent solution. One conventional heater solution includes metallized foil heaters formed from a thin metal film sandwiched in kapton film or silicone. Metallized foil heaters are useful at higher watt densities, but have excess weight, mostly in the insulation. Another conventional solution includes bare Nichrome wires integrated into a bulky enclosure to protect the ultra-high temperature wires and maintain safe operating distances. Another conventional solution includes cartridge heaters or point source heaters integrated into a thermally conductive block. These heaters have high mass and high watt densities. Finally, resistors including through hole resistors and surface mount chip resistors can serve as heaters. However, these solutions tend to have irregular shapes and/or mounting issues making uniform heating difficult.